What's the matter? Q-glasses could be a new class of solids

Aug 07, 2013

The odd microstructure of this aluminum-iron-silicon mixture is seen in this image. The round nodules are the q-glass, not crystalline but with a well-defined chemical composition. The spherical shape indicates that they grow from an initial seed. The nodules use up iron and silicon in the mixture until the surrounding concentration of aluminum gets high enough to start forming aluminum crystals, seen as long bright lines radiating from the nodules. (Color added for clarity.) Credit: Bendersky/NIST

There may be more kinds of stuff than we thought. A team of researchers has reported possible evidence for a new category of solids, things that are neither pure glasses, crystals, nor even exotic quasicrystals. Something else.

The research team from NIST, Argonne National Laboratory, France's Centre d'Élaboration de Matériaux et d'Études Structurales (CNRS) and the University of Washington have analyzed a solid alloy that they discovered in small discrete patches of a rapidly cooled mixture of aluminum, iron and silicon. The material appears to have none of the ordering of atoms found in crystals, which would make it a glass, except that it has a very defined composition and grows outward from "seeds"—things that glasses most assuredly do not do.

The solids catalog used to be pretty straightforward. Solid stuff was either a crystal or a glass. Crystals fill up space with atoms or molecules in specific, fairly rigid patterns. The positions of the atoms are fixed such that if you take any section of pure crystal and slide it up, down, in, out or sideways a given distance, it will fit perfectly in the new position. That's translational symmetry. You can also spin the crystal through certain angles and the atoms also will line up; that's rotational symmetry.

Glasses have neither symmetry. They're just a random arrangement of their components, as if you'd taken a liquid and suddenly frozen everything in place without giving the atoms a chance to get in order. Which, in fact, is how metallic glasses are made.

In the 1980s, Daniel Schectman, an Israeli then working at NIST as a guest researcher, shook up this paradigm by finding evidence for quasicrystals, a new category of solids in which the atomic composition is fixed, and the material has rotational symmetry, but weirdly not translational symmetry. There is no long-range order to the pattern of the atoms.

The new material, which the research team has provisionally dubbed a "q-glass," can be shown by X-ray diffraction to have neither rotational nor translational symmetry, just like a glass, says Levine, but regardless, the atomic arrangement apparently is not random. "As the nodule grows, every atom still knows where to go," he says.

For one thing, the q-glass seems to have a strict chemical composition, according to Levine. Seen under a microscope, it's clear that, like a crystal, the spherical q-glass regions grow outward from a seed during cooling and exclude atoms that don't fit. "It's rejecting atoms that aren't fitting into the structure, and if there's no structure, it's not going to be doing that," says Levine. "It's amazing. Everything you can think about this thing behaves like a crystal, except it isn't."

The team used a variety of sophisticated techniques at Argonne's Advanced Photon Source to rule out other possibilities. The material might, for example, be a mass of randomly arrayed crystals so small they don't show up individually under the X-ray probes. But if such crystals were there, they'd grow slowly as the stuff is annealed. That doesn't happen. "We went through the laundry list of possibilities and disproved them, one by one," says Levine.

One possibility, say the researchers, is "frustration"—two or more incompatible crystal orderings may start growing from the seeds and continually interfere with each other, destroying any long-range order. But, "one exciting possibility is that the q-glass is the first example of a 3-dimensionally ordered configuration of atoms that possesses neither translational nor rotational symmetry," says Levine. "Such structures have been theorized by mathematicians, but never before observed in nature."

Related Stories

(Phys.org) —When a molten material cools quickly, parts of it may have enough time to grow into orderly crystals. But if the cooling rate is too fast for the entire melt to crystallize, the remaining material ...

(Phys.org) —Metallic glasses are essentially a frozen, supercooled liquid. They are amorphous metals, often alloys, which are non-crystalline and therefore have a highly disordered atomic arrangement. They ...

(Phys.org) —Ever since their discovery in 1984, the burgeoning area of research looking at quasiperiodic structures has revealed astonishing opportunities in a number of areas of fundamental and applied ...

(Phys.org) —For the first time, scientists have mapped the structure of a metallic glass on the atomic scale, bringing them closer to understanding where the liquid ends and the solid begins in glassy materials.

Drawing on powerful computational tools and a state-of-the-art scanning transmission electron microscope, a team of University of Wisconsin-Madison and Iowa State University materials science and engineering researchers has ...

(Phys.org)—A new way to make glass has been discovered by a collaboration of researchers at the Universities of Düsseldorf and Bristol using a method that controls how the atoms within a substance are ...

Recommended for you

Researchers at the University of Houston have created a new thermoelectric material, intended to generate electric power from waste heat - from a vehicle tailpipe, for example, or an industrial smokestack ...

Magnetic vortex structures, so-called skyrmions, could in future store and process information very efficiently. They could also be the basis for high-frequency components. For the first time, a team of physicists ...

For almost a century, scientists have been puzzled by a process that is crucial to much of the life in Earth's oceans: Why does calcium carbonate, the tough material of seashells and corals, sometimes take ...

If you put a camera in the ice machine and watched water turn into ice, the process would look simple. But the mechanism behind liquids turning to solids is actually quite complex, and understanding it better ...

Wake up in the morning and stretch; your midsection narrows. Pull on a piece of plastic at separate ends; it becomes thinner. So does a rubber band. One might assume that when a force is applied along an ...

User comments : 0

Please sign in to add a comment.
Registration is free, and takes less than a minute.
Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.

Javascript is currently disabled in your web browser. For full site functionality, it is necessary to enable Javascript.
In order to enable it, please see these instructions.